Pyrolysis and Detoxification of Waste Electrical and Electronic Equipment (WEEE) for Feedstock
Doctoral Dissertation 2018
KTH Royal Institute of Technology
School of Industrial Engineering and Management Department of Materials Science and Engineering
Unit of Processes SE-100 44 Stockholm
Akademisk avhandling som med tillstånd av Kungliga Tekniska Högskolan i Stockholm, framlägges för offentlig granskning för avläggande av Teknologie doktorsexamen, fredagen den 30 november 2018, kl 14.00 i Kollegiesalen, Brinellvägen 8, Kungliga Tekniska Högskolan, Stockholm.
Panagiotis Evangelopoulos. Pyrolysis and detoxification of waste electrical and electronic equipment (WEEE) for feedstock recycling
KTH Royal Institute of Technology
School of Industrial Engineering and Management Department of Materials Science and Engineering Unit of Processes
SE-100 44 Stockholm, Sweden
Copyright © Panagiotis Evangelopoulos
To my beloved family
I would like to thank my supervisor, Docent Weihong Yang for giving me the opportunity to join the research group at the Unit of Process and offering me continuous support throughout my PhD studies. I would also like to specially thank my second supervisor, Asst.
Prof. Efthymios Kantarelis for the continuous guidance and the numerous discussions we had about my research.
I would also like to thank Henrik Jilvero, Marianne Gyllenhammar and Christer Forsgren from Stena Recycling International AB and Stena Technoworld AB for providing me with the WEEE materials and for the numerous emails and long talks we had about waste management and hazardous materials. Moreover, I would like to thank Shen Wu for the wonderful cooperation, building and undertaking with me the commissioning of the screw reactor. Additionally, I would like to thank Dr. Arvelakis for his guidance during the early stages of my research.
I would like to thank the Swedish Energy Agency (Energimyndigheten) and Re - Source, for the 4 years of financial support of my research through the projects “Energi- och materialåtervinning fåm WEEE” (36880-1) and “Pyrolys och dehalogenering av plastbaserat WEEE i skruvreaktor” (36880-2). I am also grateful to “Jernkontoret”, “Stiftelsen Axel Hultgrens Fond” and “Stiftelsen Ingenjör Lorens Carlson” for the travel grants that financed my travel expenses for the oral presentations at international conferences.
I would like to thank my friends and colleagues who helped me to go through the difficulties that I faced.
Finally, I would like to thank my family, who have always provided me with endless guidance and support in order to fulfil my goals and beyond. More specifically, my father for insisting to continue the PhD in spite of his critical health condition, my mother who has been constantly giving me courage to go on, my sister Iro and Takis who have been keeping company and support to our parents, when I was away. Furthermore, I would like to thank my wife’s family for their advices and guidance on my professional carrier. Finally, I would like to thank my wife Vera, who has been always next to me and without her endless love and support I would have never reached my goals and of course my son Harry who has been constantly keeping me awake during the time that I was writing the thesis.
The trends in waste electrical and electronic equipment (WEEE) generation shows that their volume constantly increases, while the current waste management technologies have proven to be insufficient in order to meet the strict criteria and the new legislations of the European Union. Pyrolysis and thermal treatment in general could be a valuable solution for closing the loop of materials and could contribute to the energy demands of modern society.
Pyrolysis as a process and combination of other pre-treatment techniques was investigated with a focus on energy production, metal separation and feedstock recycling.
In this work, several fractions of real WEEE have been tested based on the process requirements and the focus of each individual study.
Firstly, the investigation was focused on the primary products of the process, revealing most of the environmental pollutants as well as the valuable monomers that can enhance feedstock recycling. A correlation of the process’ final temperature with the evolution of the major products was performed. Moreover, a conceptual reaction mechanism of Bisphenol A decomposition was suggested based on the process products.
Then, a reduction of the bromine content of the initial WEEE fraction was achieved by solvent extraction pre-treatment. Isopropanol and toluene were tested as solvents capable of removing one of the main flame retardants at WEEE fractions, Tetrabromobisphenol A.
The results indicate that the reduction of bromine was successfully performed even at ~37%.
This result was further confirmed by the reduction or total removal of brominated species in the pyrolysis products. The toluene seems to be a valuable option for the pre-treatment, since it can be provided by the pyrolysis process itself, making the entire treatment more sustainable and in accordance with the concept of circular economy.
Density separators used in the sorting of WEEE materials usually produced high moisture content fractions. As soon as those fractions follow thermal treatment, the moisture will eventually become steam, which influences the process. Therefore, WEEE materials were pyrolysed in nitrogen and steam atmospheres and their decomposition was evaluated. Steam had a negative impact on the products, since several high molecular weight products were detected, revealing that steam limits secondary cracking reactions.
Additionally, the results show that the presence of steam complicates the separation of oils and favours the migration of antimony to the gas phase. Therefore, a drying step before using pyrolysis for this fraction is necessary.
Low temperature pyrolysis was also investigated for making the WEEE more fragile to enhance metal separation from the carbonised solid residue while the fate of bromine was also monitored. The results indicate that the separation is possible at low temperatures for minimising the energy consumption of the process but it should be at least 40 ° higher than the onset temperature of the selected material. The separation was also evaluated with fractionation of the solid residue, revealing that the produced bromine-free solid carbonised material can be further utilised for energy production.
Finally, the entire process was tested in a continuous screw reactor for overall process evaluation. The results indicate that the liquid products of pyrolysis can be used for feedstock recycling, producing necessary organic compounds that can be used for manufacturing new plastics or can be used as liquid fuel. The brominated compounds tend to migrate to the gas phase, as the temperature of the process increases, making the recycling of metals from the solid residue easier. The process in general can be self- sustained since the energy needed for the system to heat up can be covered from its gas production.
Keywords: Pyrolysis, WEEE, solvent extraction, brominated flame retardants, Tetrabromobisphenol A, Auger reactor
Baserat på de nuvarande trenderna inom avfallssektorn för elektrisk och elektronisk avfall (WEEE) behöver den nuvarande avfallshanteringen förbättras för att godkännas av nya strikare lagstiftningarna i Europeiska Unionen. Pyrolys och termisk behandling i allmänhet kan vara värdefulla tillvägagångssätt för att sluta materialkedjan för en cirkulär ekonomi samt bidra till energibehovet i det moderna samhället.
Pyrolys i kombination med andra förbehandlingstekniker har undersökts med fokus på material- och energiåtervinning samt separation av metaller. I avhandlingen har olika fraktioner av WEEE undersökts baserat på processkrav och fokuset i enskilda studier.
Initialt var den experimentella undersökningen inriktad på processens primära produkter, vilket påvisade förekomsten av flertalet miljöföroreningarna liksom värdefulla monomerer för framida materialåtervinning. Detta arbete utgjordes av en korrelativ studie mellan processens behandlingstemperatur och framställningen av de huvudsakliga produkterna. Dessutom skapades en konceptuell reaktionsmekanism för nedbrytning av bisfenol A baserat på processprodukterna.
En annan studie reducerade bromhalten i WEEE genom förbehandling i form av lösningsmedelsextraktion. Isopropanol och toluen undersöktes utifrån deras förmåga att extrahera en av de huvudsakliga flamskyddsmedlen som finns i WEEE, dvs tetrabrombisfenol A. Projektet resultatvisar att bromhalten reducerades med ca 37 %.
Detta resultat bekräftades också vid efterföljande pyrolysexperiment genom reduktion eller omätbara halter av bromerade arter i pyrolysprodukterna. Toluen tycks därför vara ett lovande alternativ för förbehandlingen och kan dessutom tillhandahållas av pyrolysprocessen själv genom att utgöra en huvudsaklig komponent i framställd pyrolysolja, vilket bidrar till en mer hållbar behandlingsmetod.
Densitetsavskiljare som används inom hanteringen av WEEE resulterar ofta i fraktioner med hög fukthalt. När sådana fraktioner utsätts för termisk behandling kommer således fukten att omvandlas till vattenånga, vilket påverkar processen. Därför gjordes experimentella försök där WEEE pyrolyserades i kvävgas och vattenånga följt av utvärdering av materialets nedbrytning i respektive miljö. Vattenånga hade negativ påverkan på pyrolysprodukterna genom ökade molekylvikter, vilket visar att vattenånga begränsar sekundära krackningsreaktioner. Dessutom visar resultaten att vattenånga komplicerar separationen av bildade oljor samt gynnar migrering av antimon från kolrest till gasfasen.
Därmed anses ett torkningssteg före pyrolys av WEEE absolut nödvändigt.
Pyrolys vid lägre temperaturer undersöktes för att studera WEEEs bräcklighet vid olika temperaturer för att förbättra metallavskiljningen från den organiska fasta restprodukten från pyrolys samt att identifiera broms fördelning bland produkterna. Resultaten indikerar att separation är möjlig vid låga temperaturer för att minimera processens energiförbrukning men minst 40 °C högre än temperaturen då materialet termiskt börjar sönderdelas. Separationen utvärderades också med fraktionering av den fasta återstoden, vilket visade att det framställda bromfria fasta produkten kan användas ytterligare för energiåtervinning.
Slutligen testades hela processen i en kontinuerlig skruvreaktor för övergripande processutvärdering. Resultaten indikerar att de flytande produkterna från pyrolys kan användas för materialåtervinning, vilket därmed utgör en råvara avorganiska föreningar som kan användas för att tillverka ny plast eller exempelvis flytande bränsle. De bromerade föreningarna i WEEE tenderar att migrera till gasfasen. Dessutom blir separationen av metaller enklare med en ökad temperatur. Processen i allmänhet kan vara självförsörjande på energi då de bildade pyrolysgaserna innehåller tillräckligt mycket energi för att värma systemet vid kontinuerlig användning.
Nyckelord: Pyrolys, WEEE, lösningsmedelsextraktion, bromerade flamskyddsmedel, tetrabrombisfenol A
Με τους ρυθμούς ανάπτυξη της τεχνολογίας σήμερα, τα Απόβλητα ειδών Ηλεκτρικού
& Ηλεκτρονικού Εξοπλισμού (ΑHHE) η waste electrical and electronic equipment (WEEE) συνεχώς αυξάνονται ενώ οι τεχνολογίες διαχείρισης και ανάκτησης υλικών πρέπει να βελτιώνονται προκειμένου να συναντήσουν τα αυστηρά κριτήρια που έχει θέσει η ευρωπαϊκή νομοθεσία. Η πυρόλυση και γενικά οι θερμοχημικές διεργασίες θα μπορούσαν να αποτελέσουν μια βιώσιμη λύση για περαιτέρω ανάκτηση των υλικών αλλά και για αξιοποίησης του ενεργειακού τους περιεχομένου.
Η πυρόλυσή αλλά και άλλες προκατεργασίες έχουν μελετηθεί πειραματικά με στόχο την παραγωγή ενέργειας, τον διαχωρισμό των μετάλλων και την ανάκτηση του οργανικού περιεχομένου των ΑΗΗΕ. Μερικά από τα πιο σημαντικά κλάσματα των ΑΗΗΕ έχουν εξεταστεί με βάση τους περιορισμούς που μπορεί να προκαλέσουν στην διεργασία.
Αρχικά, η έρευνα επικεντρώθηκε στα πρωτογενή προϊόντα της πυρόλυσης, αποκαλύπτοντας τους περιβαλλοντικούς ρύπους καθώς και τα παραγόμενα μονομερή που μπορούν να χρησιμοποιηθούν για την ανακύκλωση πρώτων υλών. Έγινε συσχέτιση της τελικής θερμοκρασίας της διεργασίας με την παραγωγή των κυριότερων προϊόντων.
Επιπλέον, προτάθηκε ένας μηχανισμός αντίδρασης της αποσύνθεσης της δισφαινόλης Α με βάση τα προϊόντα της διεργασίας.
Στη συνέχεια, η μείωση της περιεκτικότητας σε βρώμιο του αρχικού κλάσματος ΑΗΕΕ επιτεύχθηκε με προκατεργασία εκχύλισης με διαλύτη. Η ισοπροπανόλη και το τολουόλιο δοκιμάστηκαν ως διαλύτες ικανές να απομακρύνουν ένα από τα κύρια επιβραδυντικά φλόγας σε κλάσματα WEEE, την Τετραβρωμο-δισφαινόλη Α. Τα αποτελέσματα δείχνουν ότι η μείωση του βρωμίου διεξήχθη επιτυχώς ακόμη και στο ~ 37%. Αυτό το αποτέλεσμα επιβεβαιώθηκε περαιτέρω από τη μείωση ή την ολική απομάκρυνση βρωμιωμένων ειδών στα προϊόντα πυρόλυσης. Το τολουόλιο φαίνεται να αποτελεί την πιο πολύτιμη επιλογή για την προεπεξεργασία, δεδομένου ότι μπορεί να παρασχεθεί από την ίδια τη διαδικασία πυρόλυσης, καθιστώντας όλη την επεξεργασία βιώσιμη.
Η υψηλή περιεκτικότητα σε υγρασία που προέρχεται από διαχωριστές πυκνότητας διερευνήθηκε επίσης ως ένας άλλος σημαντικός περιοριστικός παράγοντας της ανακύκλωσης των ΑΗΗΕ μέσω της πυρόλυσης. Τα ΑΗΗΕ πυρολύθηκαν σε ατμόσφαιρα αζώτου και ατμού και αξιολογήθηκε η αποσύνθεση τους. Ο ατμός έδειξε αρνητική επίδραση στα προϊόντα, καθώς ανιχνεύθηκαν αρκετά προϊόντα υψηλού μοριακού βάρους, αποκαλύπτοντας ότι ο ατμός περιόριζε τις δευτερογενείς αντιδράσεις πυρόλυσης.
Επιπλέον, τα αποτελέσματα δείχνουν ότι η παρουσία ατμού περιπλέκει τον διαχωρισμό των ελαίων και ευνοεί τη μετανάστευση του αντιμονίου στην αέρια φάση. Επομένως, ένα στάδιο ξήρανσης πριν από τη χρήση πυρόλυσης για αυτό το κλάσμα είναι απολύτως απαραίτητο.
Πυρόλυση χαμηλής θερμοκρασίας διερευνήθηκε επίσης για να γίνει το ΑΗΗΕ πιο εύθραυστο για την βελτίωση του διαχωρισμού μετάλλων από το οργανικό ανθρακούχο στερεό υπόλειμμα. Τα αποτελέσματα δείχνουν ότι ο διαχωρισμός είναι εφικτός σε χαμηλές θερμοκρασίες για ελαχιστοποίηση της ενεργειακής κατανάλωσης της διεργασίας αλλά
τουλάχιστον κατά 40° υψηλότερη από τη θερμοκρασία εκκίνησης του επιλεγμένου υλικού.
Ο διαχωρισμός αξιολογήθηκε επίσης με κλασμάτωση του στερεού υπολείμματος, αποκαλύπτοντας ότι το παραγόμενο χωρίς βρώμιο στερεό ανθρακούχο υλικό μπορεί περαιτέρω να χρησιμοποιηθεί για παραγωγή ενέργειας.
Τέλος, ολόκληρη η διεργασία δοκιμάστηκε σε συνεχή κυλινδικού περιστρεφόμενου αντιδραστήρα για συνολική αξιολόγηση της διαδικασίας. Τα αποτελέσματα δείχνουν ότι τα υγρά προϊόντα πυρόλυσης μπορούν να χρησιμοποιηθούν για ανακύκλωση πρώτων υλών, δημιουργώντας τις απαραίτητες οργανικές ενώσεις που μπορούν να χρησιμοποιηθούν για την κατασκευή νέων πλαστικών ή μπορούν να χρησιμοποιηθούν ως υγρό καύσιμο. Οι βρωμιωμένες ενώσεις τείνουν να μεταναστεύουν στην αέρια φάση, καθώς η θερμοκρασία της μεθόδου αυξάνεται καθιστώντας ευκολότερη την ανακύκλωση μετάλλων από το στερεό υπόλειμμα. Η διαδικασία γενικά μπορεί να είναι αυτοσυντηρούμενη αφού η ενέργεια που απαιτείται για να θερμανθεί το σύστημα μπορεί να καλυφθεί από την παραγωγή του αερίου επεξεργασίας.
Λέξεις-κλειδιά: Πυρόλυση, ΑΗΗΕ, εκχύλιση με διαλύτη, βρωμιωμένα επιβραδυντικά φλόγας, Τετραβρωμοδιφαινόλη Α
The dissertation is based on the following supplements:
Supplement I: P. Evangelopoulos, E. Kantarelis, W. Yang, "Investigation of the thermal decomposition of printed circuit boards (PCBs) via thermogravimetric analysis (TGA) and analytical pyrolysis (Py-GC/MS)", Journal of Analytical and Applied Pyrolysis, vol. 115, s. 337-343, 2015.
Supplement II: P. Evangelopoulos, S. Arato, H. Persson, E. Kantarelis, W. Yang,
"Reduction of brominated flame retardants (BFRs) in plastics from waste electrical and electronic equipment (WEEE) by solvent extraction and the influence on their thermal decomposition", Waste Management.
Available online from 18 June 2018, In Press, Corrected Proof.
Supplement III: P. Evangelopoulos, E. Kantarelis, W. Yang, "Experimental investigation of the influence of reaction atmosphere on the pyrolysis of printed circuit boards", Applied Energy, vol. 204, s. 1065-1073, 2017.
Supplement IV: P. Evangelopoulos, N. Sophonrat, H. Jilvero, W. Yang, “Investigation on the low-temperature pyrolysis of automotive shredder residue (ASR) for energy recovery and metal recycling”, Waste Management 76, 507-515.
Supplement V: P. Evangelopoulos, S. Arvelakis, E. Kantarelis, W. Yang, “Experimental investigation of low temperature pyrolysis of printed circuit boards (PCBs) and printed circuit board components (PCB sockets)”. Submitted Journal of Hazardous Materials.
Supplement VI: P. Evangelopoulos, H. Persson, E. Kantarelis, and W. Yang, “Pyrolysis of waste electrical and electronic equipment (WEEE) on a single screw reactor for bromine-free oil production. Submitted to Energy & Fuels.
For all the supplements, I have performed the experiments, the analysis of the results and the major writing of the manuscripts.
Contribution by the author to other publications, not included in the dissertation 1. E. Kantarelis, P. Evangelopoulos, W. Yang, “Material and Energy Recovery
from Waste of Electrical and Electronic Equipment: Status, Challenges, and Opportunities”, Resource Recovery to Approach Zero Municipal Waste, 222- 263.
2. P. Evangelopoulos, E. Kantarelis, W. Yang, “Experimental investigation of pyrolysis of printed circuit boards for energy and materials recovery under nitrogen and steam atmosphere”, Energy Procedia 105, 986-991.
3. H. Persson, E. Kantarelis, P. Evangelopoulos, W. Yang, “Wood-derived acid leaching of biomass for enhanced production of sugars and sugar derivatives during pyrolysis: Influence of acidity and treatment time.” J Anal Appl Pyrolysis 2017; 127 (May):329–34.
4. H. Persson, T. Han, L. Sandström, W. Xia, P. Evangelopoulos, W. Yang
“Fractionation of liquid products from pyrolysis of lignocellulosic biomass by stepwise thermal treatment”. Energy. 2018; 154:346–51.
5. T. Han, N. Sophonrat, P. Evangelopoulos, H. Persson, W. Yang, P. Jönsson
“Evolution of sulphur during fast pyrolysis of sulfonated Kraft lignin”. J Anal Appl Pyrolysis. 2018; 133:162–8.
1. Contribution to the writing, performing the literature review and completing the final editing.
2. Writing the manuscript, performing the experiments, participating and presenting the results orally at the 8th International Conference on Applied Energy.
3. Contribution to the experimental set ups and the final editing.
4. Contribution to the final editing only.
5. Contribution to the early stages of the experimental plan, creating the method used for the analysis of the experimental findings and organising the structure of the manuscript.
1. Introduction ... 1
1.1 Objectives ... 3
1.2 Structure of the dissertation ... 4
2. Background ... 6
2.1 Waste management of WEEE fractions... 8
2.2 Pyrolysis of waste fractions ... 9
3. Experimental Procedures, Materials and Methods... 10
3.1 Pyrolysis experimental facilities ... 10
3.1.1 Analytical pyrolysis (PY-GC/MS) ... 10
3.1.2 Fixed bed reactor ... 10
3.1.3 Auger reactor ... 11
3.1.4 TGA ... 12
3.2 Material analysis ... 13
3.2.1 GC/MS ... 13
3.2.2 Titrator ... 13
3.2.3 SEM - EDS ... 13
3.2.4 XRD ... 14
3.3 Materials used ... 14
3.3.1 Printed circuit boards (PCBs) ... 14
3.3.2 Printed circuit board sockets (PCB sockets) ... 15
3.3.3 Brominated plastics, modem–WiFi plastics and brominated PCBs ... 17
3.3.4 Metal containing plastic waste ... 19
3.3.5 WEEE general fraction ... 20
4. Primary Products Investigation of Pyrolysis Process ... 22
4.1 Results and discussion ... 22
4.2 Summary ... 25
5. Effect of WEEE Pre-treatment by Solvents for Bromine Reduction ... 26
5.1 Results and discussion ... 26
5.2 Summary ... 28
6. Influence of the Pyrolysis Process from Inert and Reactive Agents ... 29
6.2 Summary ... 31
7. Low Temperature Pyrolysis for Metals and Feedstock Recycling ... 33
7.1 Results and discussion ... 33
7.2 Summary ... 38
8. Pyrolysis of WEEE in Auger Reactor ... 40
8.1 Results and discussion ... 40
8.2 Summary ... 44
9. Conclusions ... 45
10. Future Recommendations ... 47
11. References ... 48
LIST OF ABBREVIATIONS
Amu Unified atomic mass unit ASR Automotive Shredded Residue BRFs Brominated Flame Retardants
EU European Union
GC/MS Gas chromatography / Mass spectrometry HHV High Heating Value
ICP-AES Inductively coupled plasma atomic emission spectroscopy
ICP-MS Inductively coupled plasma mass spectrometry KTH Kungliga Tekniska Hogskolan
MSW Municipal Solid Waste PCB sockets Printed Circuit Board sockets PCBs Printed Circuit Boards
PCB mb Printed Circuit Boards Main Body ppm Parts per million
Py-GC/MS Pyrolysis-Gas chromatography / Mass spectroscopy
RoHS Restriction of Hazardous Substances Directive
RT Retention time
SEM - EDS Scanning electron microscope - energy- dispersive X-ray spectroscopy
TBBPA Tetrabromobisphenol A TGA Thermogravimetric Analysis
TGA DSC Thermogravimetric Analysis Differential Scanning Calorimeter
WEEE Waste electrical and electronic equipment XRD X-ray diffractometer
Waste electrical and electronic equipment (WEEE) today is the fastest growing fraction of solid waste since it has increased three times faster than the growth of average municipal waste . Uncontrolled or poor treatment of this waste fraction can lead to extremely hazardous compounds leaching into the aquifer with tremendous consequences for our ecosystem and the food chain . Special treatment of WEEE has been suggested by European and global agencies in terms of two main aspects:
Reducing the hazardous compounds which could escape into the environment.
Maximizing the recovery of both materials and energy.
The European Union has recognised the severity of the issue of WEEE by implementing directives to enhance proper handling and by setting up high recovery rates for the materials to the recyclers [3,4].
The WEEE fraction is very challenging when it comes to proper handling, since it is a highly inhomogeneous fraction and is dynamic over time. More specifically, it consists of metals, ceramic materials and plastics together with several pollutants such as heavy metals and brominated flame retardants. Recycling companies have established several techniques for partially recycling several materials by mainly mechanical means. On the other hand, there are still some problematic fractions, whose recovery rates need to be improved.
Pyrolysis of WEEE has been proposed by several researchers as a way to fulfil both aspects stated above, since the process can enhance the controlled leaks of hazardous materials, while at the same time it can produce feedstocks for maximising the recovery of materials and energy [5–7]. The two main fractions that attract the interest of recycling companies and the scientific community are metal recovery and plastic recovery. This is strongly related to the initial composition of the problematic WEEE fraction.
The metal rich WEEE fraction consists of components where the metals are strongly attached with plastics. Even though mechanical separation might have been applied, separation of the organic and inorganic parts is not possible. Therefore, the separation can be further enhanced with pyrolysis, primarily through the production of combustible gases and liquids and secondarily by allowing the metals to be further separated from the carbonaceous char.
The plastic rich WEEE fractions mainly consist of halogenated flame retarded plastics and some remaining metals. The thermal decomposition of those plastics can enhance the halogens towards specific fraction of products by adjusting the pyrolysis conditions. Then the halogens can be easily discarded and treated, allowing for the
recovery of chemical feedstocks. The general approach of the pyrolysis for energy and materials recovery is illustrated in Figure 1-1.
Figure 1-1 General approach of pyrolysis of WEEE for energy and materials recovery.
The aim of this study is to investigate the pyrolysis of WEEE as a treatment method in order to optimise the recovery of energy and material feedstocks and to minimize the release of hazardous substances into the environment. The following objectives are set so that the aim is fulfilled.
Identify the primary products and the main pollutants produced by the pyrolysis of WEEE.
Investigate the major parameters that influence the chemical recycling of WEEE.
Explore different ways of minimizing the drawbacks of the process and maximizing the recovery of energy and materials.
Investigate different methods for the removal of halogenated compounds derived from flame retardants.
Evaluate the possibility of scaling up the process.
Collect the necessary information in order to optimize the process’ feasibility.
4 1.2 Structure of the dissertation
This dissertation is organized into chapters based on the methodology used to achieve the objective of the dissertation.
Chapter 2 provides a brief overview of the technology used to approach the feedstock recycling of WEEE. The fundamentals of pyrolysis together with important facts about the conditions used are also included.
Chapter 3 summarizes the two most important aspects of the experimental investigations performed for this study, the materials and methods. In this chapter, the selection of the material used together with a detailed description of the experimental set ups is included. The material selection was vital for the dissertation since different materials were used for different studies.
Chapter 4 includes an experimental investigation of the fraction of printed circuit board, which is considered to be one of the most challenging waste streams of WEEE.
This investigation includes the identification of the primary organic compounds produced by pyrolysis at different temperature conditions.
Chapter 5 investigates the pre-treatment of several WEEE fractions through solvent extraction. The experiments include three problematic fractions of WEEE collected from the industrial plant of Stena Recycling AB located in Halmstad. The solvent extraction as a pre-treatment for the removal of the brominated flame retardant (Tetrabromobisphenol A) was investigated. In addition, the fate of bromine at the organic compounds produced by pyrolysis was investigated.
In Chapter 6, the influence of steam on the pyrolysis process was investigated, since total removal of moisture could increase the cost of the process. The WEEE fraction usually contains moisture due to the pre-treatment used for separating the heavy flame retarded plastics from the pure plastics. The experimental investigation was carried out on a fixed-bed reactor in order to investigate the influence of the process atmosphere on the gas production and differences in the solid residue were explored.
In Chapter 7, the metal recovery was investigated on the solid residue produced from low temperature pyrolysis. One of the most profitable parts for the recyclers of WEEE is the metals derived from WEEE. Pyrolysis could improve the metal recovery by enhancing the separation of the organic part of WEEE from the metals. At the same time, since pyrolysis is a mild treatment process (low temperature and inert atmosphere), the metals are not oxidized, cutting costs from processes for reduction of the metals.
Chapter 8 includes an experimental investigation of one of the main problematic WEEE fractions, rich with brominated flame retardants. The experiments tend to mimic industrial conditions in order to extract valuable data for future industrial reactor designs. The selection of a continuous reactor was necessary; therefore the experiments were carried out on a screw reactor with continuous feeding.
Supplement title Objectives I Investigation of the thermal
decomposition of printed circuit boards (PCBs) via thermogravimetric analysis (TGA) and analytical pyrolysis (Py-GC/MS)
Investigate the primary products of pyrolysis of PCBs at different temperatures
Explore the decomposition characteristics
Reveal possible reaction pathways of the decomposition
Identify the temperature window where the process could produce less pollutants II Experimental investigation of
the influence of the reaction atmosphere on the pyrolysis of printed circuit boards
Compare the decomposition of PCBs in inert and highly oxidative atmospheres
Evaluate the energy recovery from the produced gas
Investigate possible changes to the solid residue due to the different conditions applied
III Reduction of brominated flame retardants (BFRs) in plastics from waste electrical and electronic equipment (WEEE) by solvent extraction and the influence on their thermal decomposition
Perform pre-treatment of WEEE material for removal of Tetrabromobisphenol
Compare different solvents for this removal
Evaluate the removal of Tetrabromobisphenol through analytical pyrolysis
Examine the influence of removal based on their decomposition characteristics
IV Experimental investigation of low temperature pyrolysis of printed circuit boards (PCBs) and printed circuit board components (PCB sockets)
Investigation of different temperatures and retention times of pyrolysis for maximizing the yield of char for enhancing the separation of metals
Evaluate the separation of the metals from the char
V Investigation of the low- temperature pyrolysis of automotive shredder residue (ASR) for energy recovery and metal recycling
Investigation of low temperature pyrolysis at metal rich waste fractions
Evaluation of the process for the separation of organic and inorganic fractions
VI Pyrolysis of waste electrical and electronic equipment (WEEE) on a single screw reactor for bromine-free oil production
Temperature investigation for bromine-free oil production
Reveal the fate of bromine through a continued process
Yield comparison based on the mass balances
Evaluation of a continued pyrolysis process on a
In the past half a century, the demand on materials and energy has been steadily increasing due to the population growth and the improvement of living standards. This has been a driving force for humanity to change their linear way of consuming, switching to more efficient circular models of economy. Therefore, the concept of a circular economy and sustainable development have been introduced and implemented in the last few decades .
The massive consumption of resources and the increasing demand for materials and energy has led to increased volumes of waste. Several years ago waste was considered to be something that everyone was trying to discard by digging it into the ground, while now more societies think of it as a valuable resource. Urban mining is becoming increasingly popular as a concept in sustainable societies, not only for minimizing the environmental impact of waste generation but also for improving materials and energy utilization .
Waste electrical and electronic equipment (WEEE) has been one of the fastest growing fractions of municipal solid waste (3-5% per year) in the last few decades according to Eurostat statistics . Moreover, the volume of WEEE streams is going to increase in the coming years based on recent statistics, reaching up to 6.7 kg of waste per year per inhabitant as illustrated in Figure 2-1 . This fraction has increased society’s consciousness in the last few decades in two obvious ways: a) the large and increasing volume and b) the high content of hazardous materials.
Figure 2-1 Global quantity of WEEE generated based on  together with the population predictions for the coming years.
Sweden is one of the leaders in recycling in the European Union. Based on the statistics, Sweden recycled at least half of its municipal waste in 2014, but at the same time, Sweden holds second place in the highest generation of WEEE per capita (12.2
6.4 6.6 6.8 7 7.2 7.4 7.6
0 10 20 30 40 50 60
2010 2011 2012 2013 2014 2015 2016 2017 2018
E-waste generated (Mt)
Global quantity of e-waste generated
E-waste generated (Mt) E-waste generated (kg/inh.) Population (billion)
kg/capita). In Figure 2-2, the map of Europe is illustrated based on the percentage of WEEE that was collected in 2016. This shows that Sweden, even though it produces a lot of WEEE, its collection system is more efficient compared to that of other European countries.
The WEEE fraction poses several difficulties for both collection and treatment.
Moreover, this waste fraction consists of several components such as printed circuit boards, motors, pumps, batteries, lamps or bulbs, display screens, capacitors, ink or toner cartridges, asbestos and mercury switches, and also includes highly hazardous compounds. Therefore, the treatment of this waste fraction should be performed in a fully controlled environment.
Figure 2-2 EU statistics waste electrical and electronic equipment (WEEE) collection from households (Eurostat, 2016).
The European Union as well as other national and international agencies around the world has taken action against the uncontrolled disposal of this waste fraction by introducing and implementing several laws and legislations. More specifically, in 2002 the EU introduced the “Waste Electrical and Electronic Equipment Directive (WEEE Directive)” on waste electrical and electronic equipment (WEEE) which, together with
the RoHS Directive 2002/95/EC, became European Law in February 2003 . This law included all the necessary regulations that need to be followed from the member states and the categories of WEEE that need to be considered. Furthermore, the regulation was updated in 2012, setting higher goals for recovery and recycling .
2.1 Waste management of WEEE fractions
The waste hierarchy was established based on article 4 of the EU Directive 2008/98/EC. The waste should preferably follow the stream illustrated in Figure 2-3.
This means that the most favourable option is to minimize consumption in order to prevent waste generation. If some goods are being purchased but are no longer needed, then reuse could be a preferable option. This has to do with reselling electronics in the case of WEEE. On the other hand, it has been proven that with the concept of reuse and to bridge the gap of new technologies, several items of obsolete electrical and electronic equipment have been shipped to developing countries where the stream of waste management is considered to be unchartered territory. Then of course, recycling should be the next option for using the existing materials to manufacture new products.
Recovery, as the next step of waste treatment includes chemical recycling and energy recovery, while the final step of the waste hierarchy is disposal, which should be reduced to a minimum, since it can only lead to safe landfill disposal .
Figure 2-3 The waste hierarchy adopted from the EU Directive 2008/98/EC .
Disposal of the WEEE or WEEE residues is considered to be the worst solution, since volatile and non-biologically degradable materials such as cadmium, mercury and persistent Polychlorinated biphenyl (PCB) can leach into the environment from landfill sites . Moreover, leaching of other persistent compounds such as brominated flame retardants has been found in leachate from landfill sites  and has been gone up the food chain and can be even found in human breast milk at high concentrations [18, 19].
Waste recovery in terms of energy content has been a common practice for Sweden as it provides inexpensive district heating . The WEEE fraction used to follow the same route as municipal solid waste several years ago, but due to environmental risks, incineration is no longer carried out. The formation of toxic compounds released from incinerators has been correlated with WEEE fractions such as dioxins, since the high concentration of antimony and copper present in WEEE fractions favours their production [21, 22].
Another thermal treatment process aimed at the energy recovery of these fractions is gasification, which has also been investigated for the WEEE fraction. Even though the conversion of the plastic fraction to energy in terms of syngas seems promising, the high metal content of WEEE could be a limiting factor. The metals can be oxidised due to the high temperature, compelling the metals to pass through the anode stages once again and increasing the energy needed for their recovery [23, 24].
2.2 Pyrolysis of waste fractions
Pyrolysis is the thermal decomposition of organic matter in the absence of oxygen.
The word derives from the Greek word “πυρ” meaning fire and the word “λυσης” which means breaking down. Since WEEE is an inhomogeneous mixture of organic and inorganic matter, this process can enable their separation. Simultaneously, pyrolysis can provide added value materials such as reusable monomers, hydrocarbons that have carbon number distribution in the range of C1 – C50 and valuable aromatic solvents like benzene, toluene, etc.  which is in accordance with the principles of sustainable development .
Feedstock recycling is the conversion to monomer or the production of new raw materials by changing the chemical structure of plastic waste through cracking, gasification or depolymerisation, excluding energy recovery and incineration .
Pyrolysis is the main process that can enhance the feedstock recycling of waste fractions.
Moreover, this process can keep the oxidation of the metals included in the waste fractions to a minimum, which can be further purified with low energy consumption processes. Only for the aluminium, the energy savings from recycling compared to the mining of bauxite can reach up to 95% , while other metals such as copper can also save up to 85% compared to primary production .
3. Experimental Procedures, Materials and Methods
The experimental investigation of this entire dissertation was divided into sub studies. The materials and the experimental facilities used for every study are described in detail in section 3.3 - Materials used and section 3.1 - Pyrolysis experimental facilities.
3.1 Pyrolysis experimental facilities
3.1.1 Analytical pyrolysis (PY-GC/MS)
Pyrolysis-gas chromatography/mass spectrometry (PY-GC/MS) was used to identify the primary products from the pyrolysis of the WEEE materials. The system consists of the Pyrola 2000 pyrolyzer from Pyrol AB coupled with an Agilent 7890A gas chromatographer (GC) and an Agilent 5975C MSD mass spectrometer (MS).
The pyrolyzer consists of a Pt filament where the sample stands and the current passes through according to the temperature conditions required. The filament is located in a chamber, where helium (He) passes through, acting as a carrier gas. The produced volatiles are introduced to the separation column directly after their production, leaving no time for secondary reactions to occur.
3.1.2 Fixed bed reactor
The fixed bed reactor (Figure 3-1) consists of a 1kW furnace with a maximum heating rate of 50 °C/min and a 25.4 mm stainless steel tube reactor is placed inside.
The sample is placed in the middle of the tube and a thermocouple, measuring the temperature of the sample, is positioned from the top side of the reactor. The temperature of the sample is monitored throughout the entire process. Nitrogen or steam can be introduced to the reactor according to the tested experimental parameters. On the outlet of the reactor, several gas washing bottles dropped into a controlled temperature cooling bath are connected to cool down the liquid fraction produced by the process. The non-condensable gases continue to the gas collecting container, where the volume can be measured through the water displacement method or can be directly analysed online with a micro GC.
Figure 3-1 Fixed bed reactor used for the pyrolysis experiments.
3.1.3 Auger reactor
The auger reactor, illustrated in Figure 3-2, consists of a single screw feeding system, which provides continuous and stable feeding. The tested material has to be homogenous in particle size in order to ensure that the feeding is constant. Then two pneumatic valves are used which open based on a sequence in order to ensure the feeding is continuous. Moreover, nitrogen is introduced in between the two valves in order to remove any oxygen that might come together with the fed material. Then, another flow of nitrogen controls the retention time of the produced gases, which is constant for the duration of the experiment. The feeding rate chosen for this experimental campaign was 0.250 kg/h and the constant flow of nitrogen within the reactor was 3 l/min.
The entire reactor consists of three heating zones alongside the screw, which can be set to the desired temperature separately, ensuring a homogeneous temperature profile. The heating zone closer to the inlet of the reactor was always heated to the temperature of 300 °C in order to avoid fast melting of the plastic material which might be close to the inlet, leading to clogging problems and immediate shut down of the feed.
Heating zones 2 and 3 were set to 400, 500 and 600 °C, according to the experiment conditions. Furthermore, the screw rotational speed can also be adjusted, giving the user the possibility to set the retention time of the material to the desired temperature.
The retention time can vary between 30 min and 60 min based on the rotational speed
The tested material decomposed inside the reactor at the set temperature and char, liquid and gas were produced. The solid material was collected at the solid residue receiver, driven by its weight, while the rest of the products were further drifted along with the nitrogen flow to the reactor’s outlet. Then heat exchangers were placed in order to effectively cool down the condensable tars and vapours produced by the process which were collected in two glass containers. The gases were led to the outlet, while a sample was introduced to a micro GC in order to analyse their composition.
Figure 3-2 Auger or single screw reactor.
The tested WEEE fraction decomposition has been experimentally investigated in a TGA/DSC 1 – Thermogravimetric Analyzer from Mettler Toledo International Inc. The decomposition experiments underwent a nitrogen atmosphere with an initial temperature of 50 °C and a final temperature of 900 °C. Three heating rates were used:
10, 20 and 30 ° C/min.
Thermogravimetric analysis was also used to study the influence of steam on the decomposition behaviour of several WEEE fractions. The equipment used was NETZSCH STA 449 F3 Jupiter thermogravimetric capable of operating with steam as a process gas.
A constant flow of 5g/h steam was introduced at the temperature of 120 °C in order to avoid condensation on the heating chamber. The same method used for the steam experiments was also used for the experiments with an inert atmosphere in order to compare the decomposition of the material. Therefore, the material was initially at a temperature of 50 °C followed by the temperature being increased to 850 °C with heating rates of 5, 10 and 20 °C/min.
3.2 Material analysis
All the materials used for the dissertation have been analysed in terms of proximate, ultimate and elemental analysis. The analysis has been performed by a certified external company, Belab AB. The procedure followed for the analysis was the following:
The ash content has been determined based on the standard of SS-EN 14775:2009/15403:2011 using the LECO TGA 701, while for the ultimate analysis, Leco Truspec CHN was used . The oxygen was calculated by difference. For the elements of chlorine and bromine, a Thermo Scientific Dionex Aquion Ion Chromatography System was used. Finally, the trace metals elemental analysis was carried out by both ICP-AES and ICP-SMS. The trace elements were determined using 18 scans over the mass range, resulting in a total measurement of 300s. For every material, the analysis of the composition is illustrated in the tables in section 3.3 - Materials used.
For all the experiments performed on the fixed bed reactor and the screw reactor, the liquid fraction of the products was collected, measured and its composition was analysed by a gas chromatographer/mass spectrometer (GC/MS). Specifically, the same Agilent 7890A gas chromatographer (GC) and an Agilent 5975C MSD mass spectrometer (MS) as referred to in section 3.1.1 - Analytical pyrolysis (PY-GC/MS).
The liquid fraction (oils) produced by the screw reactor were analysed by an Excellence Titrator T5 for water content analysis based on the ASTM E203 standard .
The water content is a vital parameter to test the applicability of the oils produced. The lower the water content the easier it is to utilise the produced oil for liquid fuel production.
3.2.3 SEM - EDS
The scanning electron microscope (SEM) in combination with energy-dispersive X- ray spectroscopy (EDS) is a powerful tool for investigating the surface of the solid residue generated by pyrolysis. A Tabletop Microscope TM3030 was used for analysing the elemental composition of the solid residue. More specifically, the bromine and the metal content were investigated followed by an extensive statistical analysis in order to achieve high reliability and repeatability of the results. The sample preparation was only limited to gold paste for 30 seconds since the material was already conductive.
14 3.2.4 XRD
The solid residue for the experiments focusing on the steam atmosphere was also analysed by a Siemens D5000 X-ray diffractometer. The data was collected at 2θ from
~5° to 100° angles, followed by a database search for identification of the crystals. The database used was provided by Match 3.4 software.
3.3 Materials used
The composition of the WEEE fractions can vary according to the separation methods used prior to the experiments. Additionally, for all the waste fractions the problem of homogeneity composition arises since the waste is a dynamic stream depending on the collection period, the behaviour of the consumer, the strategies implemented in every country, etc. Therefore, for every study focusing on different aspects and problems that might be derived from the pyrolysis of WEEE, a different fraction of waste has been used. A common practice, applied to all the materials used, was the long sampling time, in order to ensure the composition was representative.
3.3.1 Printed circuit boards (PCBs)
The printed circuit boards (Figure 3-3) or waste circuit boards are the core component of electrical and electronic appliances . All the new cutting edge technological innovations of the last few decades have further enhanced their applications and use. The consequence is that PCBs can now be found in electrical and electronic appliances that were not present before, such as fridges, ovens, vacuum cleaners and coffee machines.
Figure 3-3 One of the printed circuit boards (PCBs) (a) and the powder obtained after milling the initial material in order to be used by Py-GC/MS.
Printed circuit boards consist of three main components: a) metallic sheets, b) glass fibbers and c) resin, mainly epoxy resin. All these components play a significant role in the PCB’s structure and mechanical and electrical properties . The recycling of this
WEEE fraction is challenging due to its compact structure that does not allow for further separation by mechanical means. Therefore, the chemical recycling can be a way to separate the prepeg waste into the main components by pyrolyzing the organic content.
The material analysis of the PCBs is presented in Table 3-1.
Table 3-1 Proximate, ultimate and elemental analysis of PCBs (Supplement I) .
Proximate Analysis (wt%)
Ash, 550oC 68.41
Volatile matter 20.15 Fixed carbon 9.85 Ultimate analysis [%wt db]
Au 6.61 Ba 1645
Pd 11.6 Pb 49611
Pt 0.0101 B 2470
Si 101855 Cd 0.23
Al 25700 Co 3.23
Ca 34000 Cu 338690
Fe 10300 Cr 237
K 300 Hg 3.65
Mg 530 Mo 0.187
Mn 78 Ni 1340
Na 852 Sn 1530
P 99.5 V 14.8
Ti 1372 Zn 9410
Sb 40.8 Ag 398
*Calculated by difference
3.3.2 Printed circuit board sockets (PCB sockets)
The printed circuit boards contain several extra components attached to the main board, which are used to connect the different components such as processors and
body of the PCBs. Based on Table 3-2, the difference lies not only in the metal content but also in the type of flame retardant used to protect those materials from igniting.
Figure 3-4 PCB sockets originated from the PCBs.
Table 3-2 Proximate, ultimate and elemental analysis of PCB sockets (Supplement III) .
Proximate Analysis (wt%)
Ash, 550oC 32.90
Volatile matter 63.30 Fixed carbon 3.80 Ultimate analysis [%wt db]
Au <0.5 Ba 691
Pd <0.5 Pb -
Pt <0.5 B 691
Si 58200 Cd -
Al 15100 Co -
Ca 29900 Cu 15700
Fe 4030 Cr 920
K 809 Hg 0.0553
Mg - Mo -
Mn - Ni 1060
Na 809 Sn 695
P 290 V -
Ti 1460 Zn 9790
Sb 24600 Ag 0.682
*Calculated by difference
3.3.3 Brominated plastics, modem–WiFi plastics and brominated PCBs One of the main drawbacks of the recycling process for plastics derived from WEEE is the bromine content. In most of the cases, brominated organic compounds are found in the pyrolysis oil. In order to study the behaviour of bromine and the fate of the brominated compounds that are produced by pyrolysis, three fractions of WEEE with relatively high bromine content were tested. The three fractions were collected from the recycling plant of Stena Recycling AB located in Halmstad.
The WEEE fractions followed different separation pathways through the recycling facility, highlighting differences both in the chemical composition and in the volatile matter content. The first fraction “Metal rich fraction” contains WEEE materials where plastic resin is attached to metallic sheets that are mainly derived from printed circuit boards (brominated PCBs). The second fraction (brominated modem-WiFi plastics) is a plastic mixture that contains a high amount of volatile matter, making their chemical recycling highly valuable. The material was derived from the covers of small appliances such as modems, WiFi routers, etc. The third fraction contains plastics with a high density and high bromine content derived from flame retardant use (brominated plastics). The analysis of these materials is presented in Table 3-3.
Table 3-3 Proximate, ultimate and elemental analysis of tested WEEE fractions (Supplement II) .
Proximate analysis (wt %) Brominated
Modem WiFi Plastics
Ash 550°C 9.70% 21.00% 79.70%
Volatile 86.50% 74.50% 17.00%
Carbon 3.80% 4.50% 3.30%
Ultimate analysis (wt %) Brominated Modem
Carbon (C) 67.40% 66.00% 12.90%
Hydrogen (H) 6.50% 6.10% 1.30%
Nitrogen (N) 2.05% 3.67% 0.47%
Chlorine (Cl) 0.96% 0.31% 0.04%
Sulphur (S) 0.06% 0.05% 0.16%
Bromine (Br) 0.78% 1.75% 1.63%
Oxygen* (O) 12.55% 1.12% 3.81%
Si 10100 25700 50960
Al 11900 13200 17136
Ca 9890 13200 33293
Fe 1650 2110 80136
K 262 259 268
Mg 2770 774 1012
Mn 136 165 436
Na 363 410 828
P 757 356 586
Ti 3400 6440 4558
Sb 1250 1190 1600
As 3.8 8.87 18
Ba 337 1070 8304
Pb 186 1890 31000
Cd 9.44 0.764 -
Co 12.6 9.56 92.4
Cu 2650 62500 310470
Cr 81.1 189 424
Hg 0.335 0.1 1
Mo 3.19 9.64 12.8
Ni 128 856 7320
Sn 93.6 1500 100071
Zn 984 9510 47286
Ag 11.8 125 2200
Au 0.183 0.1 210
Pd <0.1 - <20
Pt 0.1 - -
*Oxygen is calculated by difference
The results of the analysis are presented in Table 3-3. All three fractions of WEEE were shredded (<0.09mm) and homogenized in order to perform the experiments with representative samples. The materials are also illustrated in Figure 3-5.
A B C
Figure 3-5 The WEEE fractions used for the investigation of feedstock recycling and pretreatment for bromine content reduction a) brominated plastics, b) modem- WiFi
plastics and c) brominated PCBs
3.3.4 Metal containing plastic waste
To investigate the recovery of metals, a waste mixture from metal containing plastic waste was used with high metal content. This specific material includes metallic components embedded in the plastic material, similar to WEEE fractions. In addition, the metal content as can be seen in Table 3-4, is higher, making the investigation of metal recycling more possible.
Table 3-4 Composition of metal containing plastic waste fraction used for metal recovery investigation.
Proximate Analysis (wt%)
Ash, 550oC 43.6 Volatile matter 54.6 Fixed carbon
Ultimate analysis [%wt db]
Au <0.5 Ba 3600
Pd <0.5 Pb 1560
Pt <0.5 B 354
Si 54600 Cd 20.1
Ca 27700 Cu 2620
Fe 103000 Cr 575
K 3880 Hg 0.891
Mg 5760 Mo 64.3
Mn 1150 Ni 402
Na 6830 Sn 197
P 948 V 36.7
Ti 3720 Zn 18700
Sb 173 Ag 7.46
*Calculated by difference 3.3.5 WEEE general fraction
In the final stage of this dissertation, a continuous process has been developed to investigate the scaling up of the process in order to reveal the benefits and drawbacks.
Due to the reactor’s requirements, a general WEEE fraction was used for this investigation. The WEEE fraction was also collected from the Stena recycling collection and sorting site located in Halmstad, Sweden. The material has similarities to the
“brominated plastics” presented in section 3.3.3 and illustrated in Figure 3-5a, since it has been sorted and collected in a similar manner. On the other hand, an additional analysis has been performed. Furthermore, due to the fact that the screw reactor can process material with a specific particle size, the material used was shredded to 1-6mm in order to meet the reactor’s requirements. An extra analysis of the material was performed and is presented in Table 3-5 due to different time of collection.
Table 3-5 Proximate, ultimate and elemental analysis of the tested WEEE general fraction.
Proximate Analysis (wt%)
Ash, 550oC 8.4
Volatile matter 87.9 Fixed carbon
Ultimate analysis [%wt db]
Au <0.5 Ba 322
Pd <0.5 Pb 132
Pt <0.5 B
Si 11400 Cd 7.86
Al 2410 Co 1.91
Ca 8850 Cu 4840
Fe 335 Cr 66
K 229 Hg 0.217
Mg 1670 Mo 2.05
Mn 22.2 Ni 11.80
Na 308 Sn 353
P 1930 V 0.818
Ti 3010 Zn 1850
Sb 1630 Ag 1.41
*Calculated by difference
4. Primary Products Investigation of Pyrolysis Process
Printed circuit boards (PCBs) are one of the most challenging fractions of WEEE since the organic part is strongly bound with the inorganic materials (metals and glass fibres). Pyrolysis can enhance their separation and at the same time it can produce valuable feedstocks. The temperature conditions of pyrolysis play a significant role in the decomposition patterns that occur. The primary products that can be produced according to the temperature applied can formulate different stable products during the cooling down period. Therefore, the experimental investigation included flash pyrolysis experiments in the wide temperature range of 400 to 900 °C in order to correlate the evolution of the main pyrolysis products. At the same time, possible reaction mechanisms were revealed in order to further understand the process. This chapter is based on the journal paper by Evangelopoulos et al. (2015) which is also included in the appendix of this dissertation as Supplement I .
4.1 Results and discussion
The PCBs, presented on the 3.3.1 Printed circuit boards (PCBs), were pyrolysed both on a TGA and on the Py-GC/MS pyrolyzer described in sections 3.1.4 TGA and 3.1.1.
Analytical pyrolysis (PY-GC/MS) accordingly revealed the decomposition of this material and the yields of several products. The results indicate that due to the lack of content on volatile matter, the energy recovery is limited, since the maximum decomposition achieved was ~80%. Therefore, the amount of organics that can be utilized for energy purposes is limited.
Figure 4-1 illustrates the decomposition of the PCBs at different heating rates. Both the TGA curves and the DTG seem to be influenced by the heating rate applied. Since the devolatilisation only occurs when the vapor pressure of the volatiles is greater than the ambient pressure, the decomposition temperature seems to be higher at higher heating rates.
One important parameter revealed with this investigation is the decomposition characteristics. More specifically, the decomposition undergoes two main decomposition steps, one at the temperature range between 250 °C and 370 °C and one with a slower decomposition rate at higher temperatures. This is a characteristic decomposition pathway of phenolic resins and it has also been observed in other studies [37, 38].